Multi-physics analysis on a unimorphic piezoelectric diaphragm according to its shape and boundary conditions for the performance enhancement

A micro-viscometer for measuring viscosity change in small amount of liquid in real time has been proposed recently. The advantages of the device are the use of minimal liquid and maximized sensitivity for measuring viscosity. However, in previous research, even though the multi-physical simulation including electrical, mechanical, and acoustical phenomenon is necessary for design of micro-viscometer, only acoustical aspects have been considered. Thus, combined physical phenomena could not be reflected for an optimum design process. In this research, a multi-physical approach is developed for designing a micro-viscometer, and an optimized micro-viscometer design is proposed. The proposed method is able to capture multi-physical phenomena such as near field effect and added mass effect. It also has the advantage of flexible design of various shape and materials, leading to savings of cost and time.     

Processing and characterization of epoxy nanocomposites reinforced by cup-stacked carbon nanotubes

The effect of the dispersion, ozone treatment and concentration of cup-stacked carbon nanotubes on mechanical, electrical and thermal properties of the epoxy/CSCNT nanocomposites were investigated. Ozone treatment of carbon fibers was found to increase the surface oxygen concentration, thereby causing the contact angle between water, epoxy resin and carbon fiber to be decreased. Thus, the tensile strength, modulus and the coefficient friction of carbon fiber reinforced epoxy resin were improved. Moreover, the dispersion of fibers in polymer was increased and the electrical resistivity was decreased with the addition of filler content. The dynamic mechanical behavior of the nanocomposite sheets was studied. The storage modulus of the polymer was increased by the incorporation of CSCNTs. But the glass transition temperature decreased with increasing fiber loading for the ozone treated fiber composites. The ozone treatment did affect the morphology, mechanical and physical properties of the CSCNT.     

Colorless polyimides from 2,3,3′,4′-biphenyltetracarboxylic dianhydride (α-BPDA) and various aromatic bis(ether amine)s bearing pendent trifluoromethyl groups

A series of organosoluble and light-colored polyimides (III) was prepared from 2,3,3′,4′-biphenyltetracarboxylic dianhydride (α-BPDA) with various fluorinated aromatic bis(ether amine)s via two-step method with thermal or chemical imidization of poly(amic acid)s yielded polyimides. The III series had inherent viscosity of 0.74-1.01 dl/g and showed excellent solubility in a variety of organic solvents. They were soluble in the amide polar solvent, ether-type solvent, and chlorinated solvent. These polyimide films also showed a high optical transparency and less color intensity, with an ultraviolet-visible absorption edge of 369-382 nm and low b^* values (a yellowness index) of 5.0-11.7. Glass-transition temperature of the III series was recorded at 244-319 °C and higher than the isomeric polyimides V series. Compared with the nonfluorinated polyimides IV, the III series showed lighter-colored and lower dielectric constants and moisture absorptions. The good tensile properties and excellent thermal properties of the III series were also observed.     

Colorless and high organosoluble polyimides from 2,5-bis(3,4-dicarboxyphenoxy)-t-butylbenzene dianhydride and aromatic bis(ether amine)s bearing pendent trifluoromethyl groups

A series of polyimides III_a-h characterized by colorlessness, high transparency, high solubility, and good mechanical property, was synthesized from the aromatic dianhydride, 2,5-bis(3,4-dicarboxyphenoxy)-t-butylbenzene dianhydride (I), and various aromatic diamines (II_a-h) with pendent trifluoromethyl group via polyaddition, chemical imidization, and direct cast films. The III series showed more colorless than the polyimides (V and VI series) of 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) contained, the VI series was synthesized from the II with 6FDA. These films III had cut-off wavelengths between 371 and 376 nm, as well as b* value (a yellowness index) ranging from 3.0 to 4.7. In fact, it is so far the most colorless aromatic polyimide in our systematical researches. The III series had inherent viscosity ranging from 0.72 to 1.33 dL/g and showed excellent solubility in a variety of organic solvents. They were soluble in a concentration of 5-10% in the amide polar solvent, ether solvent, and chlorinated solvent. These films showed strength tensile of 97-123 MPa, dielectric constants of 2.78-3.28 (1 MHz), and moisture absorptions of 0.11-0.36 wt%. The glass transition temperature of the III series was recorded at 214-259 °C, the 10% weight loss temperature was over 468 °C, and the residue was more than 47% at 800 °C in nitrogen.     

Mechanochemical and Ceramic Synthesis of Cobalt Ferrite

Glass and Ceramics - The effect of mechanochemical activation on the formation of a cobalt ferrite phase from iron and cobalt oxalates was studied. X-ray phase, x-ray diffraction, and simultaneous...     

Fuzzy energy management strategy for parallel HEV based on pigeon-inspired optimization algorithm

Improvements in fuel consumption and emissions of hybrid electric vehicle (HEV) heavily depend upon an efficient energy management strategy (EMS). This paper presents an optimizing fuzzy control strategy of parallel hybrid electric vehicle employing a quantum chaotic pigeon-inspired optimization (QCPIO) algorithm. In this approach, the torque of the engine and the motor is assigned by a fuzzy torque distribution controller which is based on the battery state of charge (SoC) and the required torque of the hybrid powertrain. The rules and membership functions of the fuzzy torque distribution controller are optimized simultaneously through the use of QCPIO algorithm. The simulation ground on ADVISOR demonstrates that this EMS improves fuel economy more effectually than original fuzzy and PSO_Fuzzy EMS.     

Adaptive estimation and nonlinear variable gain compensation of the contouring error for precise parametric curve following

Contour following is one of the most important issues faced by many computer-numerical-control (CNC) machine tools to achieve high machining precision. This paper presents a new real-time error compensation method aiming at reducing the contouring error caused by facts such as servo lag and dynamics mismatch in parametric curved contour-following tasks. Due to the lack of high-precision contouring-error estimation method for free-form parametric curved toolpath, the error can hardly be compensated effectively. Therefore, an adaptive accurate contouring-error estimation algorithm is proposed first, where a tangential-error backstepping method based on Taylor’s expansion is developed to rapidly find the closest point on the parametric curve to the actual motion position. On this foundation, the contouring error is compensated using a proposed nonlinear variable-gain compensation method, where the compensation gain is obtained according to not only the contouring-error magnitude but also its direction variation. The stability of the system after compensation is analyzed afterwards according to the Jury stability criterion. By design of the compensator in accordance with the presented contouring-error compensation method as well as the stability analyzation result, the balance between the response speed and the contour control stability can be effectively made. Experimental tests demonstrate the feasibility of the presented methods in both contouring-error estimation and contour-accuracy improvement. Contributions of this research are significant for enhancing the contour-following performance of the CNC machine tools.     

Microstructure and growth kinetics of silicide coatings for TiAl alloy

In order to improve the oxidation resistance of Ti Al alloy, silicide coatings were prepared by pack cementation method at 1273, 1323, and 1373 K for 1-3 hours. Scanning electron microscopy(SEM), energy dispersive spectrometry(EDS) and X-ray diffraction(XRD) were employed to investigate the microstructures and phase constitutions of the coatings. The experimental results show that all silicon deposition coatings have multi-layer structure. The microstructure and composition of silicide coatings strongly depend on siliconizing temperatures. In order to investigate the rate controlling step of pack siliconizing on Ti Al alloy, coating growth kinetics was analyzed by measuring the mass gains per unit area of silicided samples as a function of time and temperature. The results showed that the rate controlling step was gas-phase diffusion step and the growth rate constant(k) ranged from 1.53 mg~2/(cm~4·h~2) to 2.3 mg~2/(cm~4·h~2). Activation energy(Q) for the process was calculated as 109 k J/mol, determined by Arrhenius' equation: k = k0 exp[–Q/(RT)].     

Balancing acidity and basicity for highly selective and stable modified MgO catalysts in the alkylation of phenol with methanol

The alkylation of phenol was investigated over magnesium oxide catalysts modified with the addition of small amount of vanadium, manganese or other components. The catalytic performance was strongly dependent on the kinds of dopants due to changes in the acid–base properties. The modified MgO catalysts showed an activity higher than pure MgO catalyst. V–Mn–MgO catalyst was found to be more active and selective than that of V–Mgo or Mn–MgO catalyst for 2,6-xylenol. Among the modified catalysts, V–Mn–MgO catalyst was excellent in both phenol conversion and the selectivity to 2,6-xylenol. The alkylation of phenol in ortho position was explained in the acid–base property of mixed oxide. Phenol conversion and 2,6-xylenol selectivity increased with acidity, whereas the selectivity to o-cresol decreased because of the nature of the series reaction (phenol→o-cresol→2,6-xylenol→2,4,6-trimethylphenol (2,4,6-TMP)). Na–Mn–MgO catalyst prepared to achieve a balance between acidity and basicity was not deactivated and highly selective to o-cresol and 2,6-xylenol. Reaction temperature, feed composition and space velocity also significantly influenced the conversion and the selectivity in the alkylation of phenol.